1. Field of the Invention
The present invention relates to a radiographic image capturing apparatus for compressing and securing an object to be examined of a subject between an image capturing base and a compression plate, then irradiating the object to be examined with radiation, and converting the radiation that has passed through the object to be examined into a radiographic image.
2. Description of the Related Art
There have heretofore been developed biopsy apparatus for sampling tissue of a biopsy region (e.g., a lesion region in a subject's breast) contained within an object to be examined of the subject, and thoroughly examining the sampled tissue to perform a disease diagnosis.
Such a biopsy apparatus is incorporated in a radiographic image capturing apparatus for capturing radiographic images of the object to be examined. The radiographic image capturing apparatus, with the biopsy apparatus incorporated therein, operates as follows. First, an object to be examined of a subject is compressed between an image capturing base and a compression plate, and the object is irradiated with radiation. Radiation that has passed through the object to be examined is converted into a radiographic image by a radiation detector, which is housed in the image capturing base. Based on the radiographic image, the position of a biopsy region in the object to be examined is calculated. Then, based on the calculated position of the biopsy region, a biopsy needle is passed through an opening provided in the compression plate in order to pierce the biopsy region, whereupon a tissue sample of the biopsy region is removed.
The opening is relatively small, e.g., the opening is a rectangular opening having a size of 5 cm×5 cm, which is just large enough to allow the biopsy needle to pass therethrough in order to remove a tissue sample of the biopsy region, but also is small enough to allow the compression plate to reliably compress the object to be examined. A region of the object to be examined, which faces the opening, serves as an examinable region from which the tissue sample can be removed. A region of the radiation detector, which is irradiated with radiation that has passed through the examinable region, serves as a radiation detecting region (image capturing region), which converts the radiation into a radiographic image corresponding to the examinable region.
Known forms of radiation detectors include a conventional radiation film for recording a radiographic image by exposure to radiation, and a stimulable phosphor panel for storing radiation energy representing the radiographic image in a phosphor, and thereafter reproducing the radiographic image as stimulated light by applying stimulating light to the phosphor. The radiation film, with the radiographic image recorded therein, is supplied to a developing device in order to develop the radiographic image. Alternatively, the stimulable phosphor panel is supplied to a reading device in order to read the radiographic image as a visible image.
In recent years, direct-conversion-type radiation detectors have been developed for directly converting radiation into electric signals, or indirect-conversion-type radiation detectors, which comprise a scintillator for temporarily converting radiation into visible light together with solid-state detectors that convert the visible light into electric signals in order to read the detected radiation image information. Such radiation detectors are widely used as radiation detectors for use in radiographic image capturing apparatus, because they are capable of shortening the time period required after the radiographic image of a subject has been captured and until the captured radiographic image is confirmed by a doctor or radiological technician.
Radiographic image capturing apparatus, which incorporate biopsy apparatus according to the related art, employ a CCD (Charge-Coupled Device) image sensor therein for reading an electric signal (electric charges), because the examinable region to be handled is very small, and the radiation detector that is used should be of a small size in order to match the examinable region. These radiographic image capturing apparatus are called SFDM (Small Field Digital Mammography) radiographic image capturing apparatus (mammographic image capturing apparatus).
It is a general practice to capture an image of an object to be examined as a CC (CranioCaudal) view by irradiating the subject to be examined, who is in a seated position, with radiation emitted from a radiation source positioned above the subject. In such an image capturing mode, the examinable region and the radiation detecting region are set near a central position on the image capturing base close to the subject. Further, the object to be examined is placed over the central position on the image capturing base, and the object is compressed and secured from above by the compression plate. The radiation source has a central angle set on a vertical axis of the image capturing base, which passes through the central position. The object to be examined, the central position, and the central angle are fixed to or set on the vertical axis.
To capture stereographic images as CC views, the radiation source is turned about a central position to assume predetermined angles (+θ1 and −θ1 in FIG. 4 of the accompanying drawings) from the central angle. When the radiation source is positioned at such angles, which are symmetrical with respect to the subject, the radiation source applies radiation to the object to the examined. When the radiation source is turned from the central angle (the aforementioned vertical axis), the radiation source possibly may come into contact with the head of the subject. In order to prevent the radiation source from contacting the head of the subject, the head of the subject needs to be spaced from the radiation source while stereographic images of the object to the examined are captured (see FIG. 5 of the accompanying drawings). During the stereographic image capturing process, therefore, and while tissue is being sampled from the object to be examined by a biopsy needle, the subject is required to keep her head uncomfortably tilted for a long period of time, e.g., from 30 minutes to 40 minutes.
In recent years, radiographic image capturing apparatus have become available on the market, which employ a direct-conversion-type radiation detector or an indirect-conversion-type radiation detector, as described above. Radiation detectors for use in such radiographic image capturing apparatus have a relatively large radiation detecting region, having a size of 18 cm×24 cm or 24 cm×30 cm, for example. Such radiographic image capturing apparatus are referred to as FFDM (Full Field Digital Mammography) radiographic image capturing apparatus, having a large examinable region and a large radiation detecting region. However, since the region of an object to be examined, which corresponds to an opening defined in the compression plate, serves as an examinable region, the examinable region of the object to be examined by the FFDM radiographic image capturing apparatus still remains relatively small.
Technologies concerning radiographic image capturing apparatus (mammographic image capturing apparatus) for capturing radiographic images of breasts, which define objects to be examined, are disclosed in Japanese Laid-Open Patent Publication No. 2007-125367 and U.S. Pat. No. 7,443,949. In Japanese Laid-Open Patent publication No. 2007-125367, it has been proposed to change relative positions of a radiation source and an image capturing base in a direction along the subject, depending on the size of the breast and the direction in which a radiographic image thereof is to be captured. In U.S. Pat. No. 7,443,949, a compression plate is proposed, which is movable in a direction along the subject.
In the radiographic image capturing apparatus according to the related art, as described above, the object to be examined is compressed and secured at a central position on the image capturing base close to the subject, and the vertical axis of the image capturing base, which passes through the central position, is set as the central axis of the radiation source. Accordingly, the central position, the object to be examined, and the central angle are fixed to or set on the same vertical axis. Consequently, the subject is required to assume an uncomfortable attitude in order to avoid obstructing the radiation source, which is turned symmetrically (equally) to the left and right with respect to the subject.
According to the technology disclosed in Japanese Laid-Open Patent Publication No. 2007-125367, when relative positions of the radiation source and the image capturing base are changed along the subject depending on the size of the breast and the direction in which the radiographic image thereof is captured, the object to be examined is off-center a given distance on the image capturing base from the central position in a direction along the subject. Further, the radiation source also is off-center a given distance from the vertical axis, in the same direction along the subject as the direction in which the object to be examined is off-center. Therefore, after the object to be examined and the radiation source have been off-center, the object to be examined and the central angle are made coaxial with each other. During the process of capturing stereographic images, the subject also is required to assume an uncomfortable attitude in order to avoid obstructing the radiation source, which is turned symmetrically (equally) to the left and right with respect to the subject.
According to the technology disclosed in U.S. Pat. No. 7,443,949, the compression plate is moved depending on the direction in which the object to be examined is imaged. However, there is nothing proposed in this technology concerning ways for allowing the subject to maintain a comfortable attitude, while radiographic images of an object to be examined are captured and tissue is sampled from a biopsy region in the object of examination.